In the link you provided the author says: 'The important thing to get absolutely clear is that a spring with lower rate (softer) can apply just as much force as a higher rate (stiffer) spring, it just needs to be compressed further to do it.' If I am reading this correctly, he basically says that preload does change spring rate.

I suggest you read the second page:

"Note that, with some exceptions, that’s all it does. Preload makes the bike sit higher, or lower. It does not make the spring stiffer. So if someone tells you that you should reduce your preload to make the bike feel less harsh, they probably don’t have a clue."

Let's try this. Imagine a spring. Imagine the spring on end and you sitting on it. It will compress. Let's say it compresses 50mm.

Now imagine putting a G-clamp on the spring and compressing it so that it's compressed by 25mm. Then (avoiding the G-clamp) sit on it again. How much will the total compression be? And will that initial compression make any difference to the bounciness of the spring?

"Note that, with some exceptions, that’s all it does. Preload makes the bike sit higher, or lower. It does not make the spring stiffer. So if someone tells you that you should reduce your preload to make the bike feel less harsh, they probably don’t have a clue."

Let's try this. Imagine a spring. Imagine the spring on end and you sitting on it. It will compress. Let's say it compresses 50mm.

Now imagine putting a G-clamp on the spring and compressing it so that it's compressed by 25mm. Then (avoiding the G-clamp) sit on it again. How much will the total compression be? And will that initial compression make any difference to the bounciness of the spring?

It’s simple physics. Look up Hooke’s law.

The force a spring applies is equal to the spring constant (or spring rate as labeled on this thread) times the “displacement squared”, with the displacement being the distance the spring is compressed from its equilibrium length (or stretched, but that’s not relevant to bike suspension).

The end result is: yes, if you increase your preload you will feel a stiffer or harsher suspension. That’s because the starting point of the spring is far from equilibrium and any additional load only makes it further away and therefore “harsher”.

The force a spring applies is equal to the spring constant (or spring rate as labeled on this thread) times the “displacement squared”, with the displacement being the distance the spring is compressed from its equilibrium length (or stretched, but that’s not relevant to bike suspension).

The end result is: yes, if you increase your preload you will feel a stiffer or harsher suspension. That’s because the starting point of the spring is far from equilibrium and any additional load only makes it further away and therefore “harsher”.

I understand simple physics. It's a good job one of us does. It's not displacement squared. Assuming the spring in tension doesn't get to the elastic limit, nor in compression get to coil binding, displacement is directly proportional to force. So increasing preload just changes ride height. If you increase the preload to the point where the displacement is the same as would be produced by your weight, the bike won't sag when you sit on it. Increase it beyond that and the suspension won't move until you hit a significant bump. That's not stiffer, that's simply immobilised.

Oops, my bad. I made one typo by adding the word “squared” in my post. That doesn’t change anything else I said in my statement. It’s just like the internet for people to find something wrong and jump all over it.

(For what it’s worth, I must have had potential energy in the back of my mind while typing, which does in fact go like the “displacement squared”).